SECTION III. PRINCIPLES OF OPERATION - TM-55-1905-223-24-170019

TM 55-1905-223-24-17

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Safety, Care, and Handling. Safety precautions must be observed at all times while performing

maintenance.

General WARNINGS and first-aid data appear in the front of this manual. Review all

safety information before starting any task. Carefully read through an entire maintenance procedure

before performing any maintenance function. Make sure the task can be done safely. All WARNINGS,

CAUTIONS, and NOTES are of great importance to your safety and the safety of the equipment.

SECTION III. PRINCIPLES OF OPERATION

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Supply System General. The heating, ventilation, and air conditioning process begins as weather air

enters the HVAC supply intakes. Initial air conditioning begins with the air being filtered. Filters are

located in each recirculation system. In the heating cycle, air in the supply intake is heated by an

electric preheater which is thermostatically controlled. Supply fans move the air through the supply

ducts to ventilate compartments and to heat or cool the air. Natural air supply to toilet and shower

spaces is through door undercuts or door louvers. FIGURE 1-2 shows a typical ventilation arrangement

for heating and cooling. Refer to TM 55-1905-223-10 for actual arrangement of heating, ventilation, and

cooling equipment in each compartment aboard the vessel.

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Supply Air System. Supply air, which is weather air, is drawn into the vessel by the ventilation supply

fans. The air intake trunks (ducts) are the major supply systems feeding air into the vessel. Each trunk

has an associated weather opening in addition to a supply air fan. Downstream of the air intake,

electric heaters are mounted in the ducts with thermostatic controls set to activate only in cold weather.

The air supply trunk serves more than one ventilation or air conditioning system within the vessel. An

electric heater in the intake duct serves as a preheater and is energized by a thermostat when the

incoming outside air is below the thermostat set point. Heating the air as it enters the vessel eliminates

duct sweating that would otherwise occur in cold weather. The supply system provides fresh outside air

to ventilated compartments and replenishes air to air conditioned compartments.

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